Blood vessel replacing materials have been developed to replace the damaged parts of arteries by atherosclerosis or aneurysm disease of vascular system. Early studies of scaffolds for blood vessel regeneration using tissue engineering were mainly studies of preparing collagens, or biodegradable polymers such as natural polymers or PGA in the tube form; seeding smooth muscle cells or endothelial cells making up vascular tissues thereon followed by culturing them in vitro for a certain period to have some mechanical strength; and then transplanting thereof in vivo.
However, the replacement materials made with the biodegradable polymers had a problem of severe blood-leakage in the early stage of in vivo transplantation because they were prepared by methods preparing porous woven fabrics. In order to compensate the problem, surface treatment studies such as blood clotting on the vessel surface in advance or collagen coating were conducted, but their result were not satisfactory. Further, the blood vessel replacing materials have severe compliance mismatch (elasticity difference) which acts as the major cause of artificial vascular occlusion and fracture. It is known that their compliances are usually one tenth of those of arteries.
Then, as a block copolymer showing biocompatibility and antithrombotic activity at the same time, SPEU (segmented polyether urethane) was used, but it was impossible to use for a long time because it caused calcification when it was transplanted in vivo.
To solve these problems, tissue engineering techniques were developed to make the environment similar with intravascular environment by culturing vascular endothelial cells in an artificial blood vessel.
As conventional biodegradable materials, a tube-type scaffold prepared by winding polyglycolic acid (PGA) non-woven fabric or poly-L-lactic acid (PLLA) woven fabric to a cylindrical shaft followed by stitching up with a suture to maintain a tube shape like the shape of the blood vessel of a living body, or prepared by soaking a PGA or PLLA mesh to a solution dissolving a polymer showing completely different dissolution property therewith such as poly-L-lactide-co-caprolactone (PLCL) followed by freeze-drying is being used.
Likewise, in case of the tube-type scaffold, a method for forming pores using poly-L-lactide-co-caprolactone (PLCL) by freeze drying is being used, but PGA or PLLA has problems of much lower elasticity than PLCL, difficulty to control degradation rate and the like.
Further, structure of the scaffold such as pore size has a limit to playing a role of an artificial blood vessel without blood-leakage under high pressure. It is preferred that the pore size of the inner part of the artificial scaffold for blood regeneration is small enough to block the blood-leakage through the pores in the blood vessel wall when blood circulates, and the pore size of the outer part thereof is big enough to make cell attachment and proliferation in the blood vessel cure process easy.
In addition, an artificial blood vessel prepared with only PLCL is mainly made by a method such as freeze-drying, casting, extruding and the like, and the made artificial blood vessel has drawbacks of low cell seeding efficiency and mechanical strength.
Therefore, there has been a demand to develop a tissue engineering porous scaffold for an artificial vessel having high elasticity and excellent mechanical strength.
Meanwhile, the electrospinning process is a process to spin a low density polymer into the fiber form in a flash using high-voltage electrostatic force by applying larger electrostatic force than the surface tension in the polymer. Recently, it is used to prepare nanometer-grade fibers, and studies thereof are actively progressing. The nano-fibers can provide various physical properties which can't be obtained from the existing fibers, and a web consisting of the nano-fibers is a membrane-type material having porosity and is very useful to various fields such as filters, wound dressings, artificial scaffolds and the like.